Two Packs, One Boundary

You'll learnto draw the system boundary and read the sign of ΔH from which way heat crosses it.

Squeeze an instant cold pack and it plunges to 2 °C. Squeeze a hand warmer and it climbs to 54 °C. Both thermometers moved, but only one of those packs took energy in, and which one is settled by where you draw the boundary. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · ΔH_soln(NH₄NO₃) = +25.7 kJ/mol · ΔH_soln(CaCl₂) = −82.8 kJ/mol · v4

two packs · one boundary · which way the energy crosses

Before you start

What you're looking at

Two cracked packs side by side: a cold pack falling toward 2 °C and a hand warmer climbing to 54 °C.

The question

Both change temperature — but which pack actually absorbed energy?

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